Dosimetry generally refers to the measurement of a long term absorbed radiation dose, rather than some momentary radiation quantity or rate. A dosimetry device counts the total radiation dose over some time interval. Detection of the radiation is based on the interaction between the radiation and some material. This interaction can cause physical, chemical or biological changes depending on the nature of the material and the amount of the radiation energy absorbed into the material.
There are a number of different dosimetry methods currently used. For example, calorimetry is based on the ability of radiation to heat water, chemical dosimetry is based on the ionization ability of radiation in water, film dosimetry utilizes the darkening of a film caused by ionizing radiation and thermoluminescent dosimetry (TLD) utilizes thermally addressable energy generated by the radiation which is trapped or stored within a thermoluminescent material.
When a thermoluminescent material is irradiated, part of the absorbed energy is preserved in meta-stable energy levels of electron bands. The preserved energy may later be released by heating the material. Part of the released energy can be detected as visible light, and the amount of light that is detected can be correlated to a dose of radiation exposure.
Thermoluminescence is most commonly observed in crystalline materials which provide energy levels, or bands within an inorganic crystal lattice, where electrons and holes can be stored in one or more meta-stable states. For example, when an electron in a valence band receives enough energy it may advance to the conduction band. At the same time, a hole is formed to the valence band. In general these states are not stable. However, meta-stable energy levels or traps are formed between the conduction and valence band by adding some chemical impurities or by causing defects in the lattice structure, allowing meta-stable electrons and holes to remain trapped. When a thermoluminescent material is heated, the trapped electrons and holes are released and recombine resulting in the emission of detectable light which is then used to determine the dose of the radiation exposure.
A particularly sensitive thermoluminescent material is lithium-fluoride, which is doped with magnesium and titanium (LiF:Mg,Ti dosimeter). Thermoluminescent dosimetry can be used in a number of radiation measuring and monitoring applications including, personnel radiation monitoring, environmental radiation monitoring, radio-therapy monitoring and in scientific research, including geology. Therefore, there is a continued need to develop new devices, methods and systems for accurately and efficiently monitoring and measuring radiation using thermoluminescent dosimetry and thermoluminescent techniques.